A radio-controlled timepiece receives a standard signal including time information and date information, and then, on the basis of the information included in this standard signal, driving means such as a motor forcefully displaces the time-indicating hands such as the hour hand, the minute hand, and the sweep hand, so that the time-indicating hands indicate the correct time corresponding to the information included in the standard signal.
Carrying out time-calibrating operation in this way at least once a day enables the radio-controlled timepiece to always show the correct time.
Meanwhile, each radio-controlled timepiece has an antenna built therein for receiving the standard signal. At the early stage of development, the radio-controlled timepiece used to have a case made, at least partially, of resin so as to allow its antenna to be more sensitive to radio waves.
The appearance of a case made of resin is, however, less attractive than that of a case made of metal. For this reason, many recent radio-controlled timepieces have employed metal as a material for their cases.
An antenna is less sensitive to signals when built in a metal case than when built in a resin case. Thus, various improvements have been made in an antenna itself to increase the reception sensitivity.
For example, a technique to improve the reception sensitivity is proposed (see Patent Document 1). In the technique, an antenna core includes: a coiled portion that is wound with a coil; and extending portions that protrude respectively towards their corresponding end portions of the antenna core. The extending portions are bent towards the windshield glass which allows the standard signals to pass therethrough relatively easily.
In addition, another technique to improve the reception sensitivity is proposed (see Patent Document 2). In the technique, an antenna core includes: a coiled portion that is wound with a coil; and extending portions located respectively on the end portions of the antenna core, and respectively connected to radio-wave acquisition portions each of which is larger in size than the corresponding portion.
Patent Document 1: JP-A-2006-153752
Patent Document 2: JP-A-2004-235701
It is difficult, however, to bend the antenna core because the antenna core is made of a brittle material, such as an amorphous material. Even if the antenna core is formed as a laminate of plural thin plates as disclosed in Patent Document 1, this antenna core, however, can be successfully bent without breakage only by an extremely small curvature. For this reason, it is difficult to greatly improve the reception sensitivity.
It is true, on the other hand, that providing radio-wave acquisition portions that are larger in size than the extension portions of the antenna core can enhance the reception sensitivity as shown in Patent Document 2. However, the accomplished enhancement in the reception sensitivity is not significant, because the antenna core and the radio-wave acquisition portions are placed within a single plane. Therefore, there still remains a demand for further enhancement in the reception sensitivity.
Simply increasing the size of radio-wave acquisition portions causes various problems. For example, the placement of the antenna is restricted within a limited space in the timepiece case. If the radio-wave acquisition portions are disposed too close to the timepiece case made of metal, a loss is caused by an eddy current. A contact of the radio-wave acquisition portions with the metal case causes an eddy current to flow through the metal case. In addition, the larger radio-wave acquisition portions also result in less efficient use of space to accommodate the antenna in the case.
The present invention made in view of the foregoing circumstances aims to provide a radio-controlled timepiece capable of further enhancing the reception sensitivity and to provide a method of assembling the same.